In directional drilling, an oil and gas well is drilled to a selected depth using a drilling motor assembly at the end of flexible drill string. Once the selected depth is achieved the drilling motor assembly is then diverted at an angle across an oil or gas bearing formation until the drilling motor assembly is in a horizontal orientation. The drilling motor assembly generally consists of a motor unit, a drive linkage, a bearing assembly and a drill bit. The motor unit includes a drilling fluid activated rotor that moves in an eccentric fashion within a stator housing. The drive linkage unit translates the eccentric rotation of the rotor into a rotational movement needed to turn the drill bit, through use of a drive shaft with a universal joint attachment. The drill bit is indirectly mounted to one end of the drive linkage via a bearing assembly. The bearing assembly has thrust and radial bearings to withstand the radial and thrust loading that the drill bit is subjected to when drilling through earth formations.
For years shock tools have been used when drilling oil and gas wells to lessen shock loading and thereby prolong the useful life of the drill bit. With directional drilling shock tools are generally not used, as they add to the length of the drilling motor assembly and limit the angle at which the drilling motor can be steered from a vertical drilling mode to a horizontal drilling mode.